Electromechanical devices having a rotor driven in discrete steps by the application of electrical current to various fixed electromagnets, and the interaction of those electromagnets with a plurality of movable permanent magnets or other electromagnets are known in the art. Such devices are known as stepper motors.
U.S. Pat. No. 5,448,117 to Elliot describes a stepper motor where the application of current to coils of the fixed electromagnets in accordance with a specific sequence results in continuous rotation of a rotor on which the movable magnets are mounted. However, the manner in which this is done is very complex. There is a stator 12, a rotor 14 and an orbiting ring 16. There are a plurality of electromagnets having coils 58 that extend radially outward as shown in FIG. 3 of that patent. The coils are energized so that adjacent magnetic poles 54 are opposite in polarity, and the polarity of poles is switched. Pairs of poles are cooperatively energized. When two adjacent coils are energized there is a magnetic flux path established between them due to there being an opposite polarity on either side of the air gap between each pair of poles and the adjacent portions of the armature ring 48. Thus, there is a strong magnetic force between the adjacent cooperating poles and the adjacent part of the armature ring 48 which pulls the adjacent part of the armature ring against those poles. Thus, an armature ring 48 is held against the ends of two cooperating poles 54.
To achieve rotational force of the stepper motor electrical current is applied to the coils of the electromagnets in a timed sequence. The interruption of current through one coil of a first pair of adjacent coils, but not the other coil of the pair, together with the application of current through one of the two coils of an adjacent second pair of coils, but not the other coil of the pair, results in a rocking movement of the orbiting ring in that the air gap between orbiting ring and the one of the two coils of the second adjacent pair of coils is closed while the air gap between the coil of the first pair of adjacent coils is opened. This rocking action results in the orbiting ring being moved between a number of stable positions. “The rotational component of the rotational motion of orbiting ring 16 is transferred to rotational motion of drive shaft 34 by means of contact of the various rollers 46, rotatably mounted on ring 16, and apertures 45 in drive plate 36.” “Movement of orbiting ring 16 to the next stable position includes a rotational movement of the ring 16 with a roller 46 rolling in contact with the adjacent surface of an aperture 45. As the contacting roller 46 moves out of contact, another roller 46 comes into contact with another aperture 45. Since there is an overall rotational component to the motion of orbiting ring 16, an overall rotation is imparted to drive plate 36 by rollers 46 coming successively into contact with the surfaces of apertures 45. Alternatively, projections similar to rollers 46 may extend radially outward from ring 16 to radially inward facing apertures on drive wheel concentric with ring 16.” This is a very complex operation.
In an alternative embodiment described in the Elliot patent “the cumulative rotation of ring 16 is transferred into rotary motion by the operation of rollers 46 in slots 45 of drive plate 36 . . . ” Thus the method by which rotational motion is achieved in the '117 patent is very complex.
Thus, there is a need in the prior art for a simplified way to achieve smooth, continuous rotational motion with a rotary electromagnetic device that has a rotor driven in discrete steps by the application of electrical current to various fixed electromagnets, and the interaction of those electromagnets with a plurality of movable permanent magnets or other electromagnets.